Numerous surgical techniques have been developped for the treatment of chondral and osteochondral defects of the knee. Among those techniques autologous chondrocyte transplantation (ACT) was promising but have potential drawbacks. A novel development by TBF is available. The aim of this randomized trial is to compared this new ACT technique to mosaicoplasty. Final outcomes were measured at 2 years using clinical evaluation scoring system (International Knee Documentation Committee), MRI and arthroscopy with biopsy. 64 patients are needed to detect a mean IKDC difference of at least 15 points with 90% power at a 5% alpha level. Twelve surgical centers in France are involved.